It is known from our UK Patent No. 2229660B and our copending European patent Application No. 92917959.6 and from Engelbrecht U.S. Pat. No. 4,248,232 and Hood U.S. Des 341,202 that the local heating effect associated with the application of ultrasound to plastics materials can be employed to soften and effect the removal of bone cement during revision arthroplasty. Specifically, it has been shown in our previous patent and patent applications that a fundamental requirement of the cement removal technique is to influence the flow of softened material so that a small quantity of cement can be isolated and retained to be captured in the head of the activated instrument in order to extract it efficiently from the operating site, over a series of penetrating cycles. An important characteristic of such instruments is the presence of an axisymmetric disc close to the distal end of the instrument, and critically, of one or more connecting ports or passages parts between the distal face and an annular cavity proximal to said disc.
It is also known from our application No. EP 92917959.6 that the flow of softened cement is encouraged by the use of an annular cutting edge optionally incorporating a taper either towards or away from the distal end of the probe.